1. Field of the Invention
The present invention relates to an optical sheet, a backlight assembly having the optical sheet and a liquid crystal display apparatus having the optical sheet. More particularly, the present invention relates to an optical sheet having different light-concentrating efficiencies according to direction, a backlight assembly having the optical sheet and a display device having the optical sheet.
2. Description of the Related Art
An optical sheet is applied to a liquid crystal display (“LCD”) apparatus in order to enhance optical properties, such as brightness, front-view brightness, etc., of light supplied to a display panel. The optical sheet has a structure having an ultraviolet-curing resin laminated on a base film including polyester. The base film has at least one adhesive surface.
A prism sheet, which is a type of optical sheet, concentrates light in a perpendicular direction and enhances front-view brightness. A prism sheet shown in FIG. 10 of U.S. Pat. No. 5,600,455 includes a plurality of prisms. Each of the prisms is extended in one direction and has an isosceles triangular-shaped cross-section. Therefore, the prism sheet can concentrate light of which the direction is in a first imaginary plane that is substantially perpendicular to a longitudinal direction of the prisms, but the prism sheet cannot concentrate light of which the direction is in a second imaginary plane that is substantially parallel to the longitudinal direction of the prisms.
Therefore, a conventional display apparatus employs two prism sheets. The two prism sheets of the conventional display apparatus are arranged such that a longitudinal direction of the prisms of a first prism sheet is substantially perpendicular to that of a second prism sheet. However, the display apparatus having two prism sheets is disadvantageous with respect to the cost and size of the display apparatus.
In order to solve the above-mentioned problem, an optical sheet capable of concentrating light in both directions perpendicular to each other in the plane of the optical sheet has been developed. The optical sheet includes a plurality of light-concentrating protrusions, each of which has a pyramid shape. However, the optical sheet has a constant light-concentrating efficiency according to the directions substantially perpendicular to each other in the plane of the optical sheet. Also, a display device employing two stacked prism sheets having the protrusions, each of which has a pyramid shape, displays a moiré pattern.